JVM28——GC调优前序知识

(1) 常用命令

jvm调优需要对于一些常用的内存设置参数熟悉，可以查阅oracle官网。或使用命令java -XX:+PrintFlagsFinal -version | findstr "GC"查看jvm中与GC相关的虚拟机参数。

查看的结果示例如下。

java version "16.0.2" 2021-07-20
Java(TM) SE Runtime Environment (build 16.0.2+7-67)
Java HotSpot(TM) 64-Bit Server VM (build 16.0.2+7-67, mixed mode, sharing)
    uintx AdaptiveSizeMajorGCDecayTimeScale        = 10                                        {product} {default}
     uint ConcGCThreads                            = 3                                         {product} {ergonomic}
     bool DisableExplicitGC                        = false                                     {product} {default}
     bool ExplicitGCInvokesConcurrent              = false                                     {product} {default}
    uintx G1MixedGCCountTarget                     = 8                                         {product} {default}
    uintx G1PeriodicGCInterval                     = 0                                      {manageable} {default}
     bool G1PeriodicGCInvokesConcurrent            = true                                      {product} {default}
   double G1PeriodicGCSystemLoadThreshold          = 0.000000                               {manageable} {default}
    uintx GCDrainStackTargetSize                   = 64                                        {product} {ergonomic}
    uintx GCHeapFreeLimit                          = 2                                         {product} {default}
    uintx GCLockerEdenExpansionPercent             = 5                                         {product} {default}
    uintx GCPauseIntervalMillis                    = 201                                       {product} {default}
    uintx GCTimeLimit                              = 98                                        {product} {default}
    uintx GCTimeRatio                              = 12                                        {product} {default}
     bool HeapDumpAfterFullGC                      = false                                  {manageable} {default}
     bool HeapDumpBeforeFullGC                     = false                                  {manageable} {default}
   size_t HeapSizePerGCThread                      = 43620760                                  {product} {default}
    uintx MaxGCMinorPauseMillis                    = 18446744073709551615                      {product} {default}
    uintx MaxGCPauseMillis                         = 200                                       {product} {default}
      int ParGCArrayScanChunk                      = 50                                        {product} {default}
    uintx ParallelGCBufferWastePct                 = 10                                        {product} {default}
     uint ParallelGCThreads                        = 13                                        {product} {default}
     bool PrintGC                                  = false                                     {product} {default}
     bool PrintGCDetails                           = false                                     {product} {default}
     bool ScavengeBeforeFullGC                     = false                                     {product} {default}
     bool UseAdaptiveSizeDecayMajorGCCost          = true                                      {product} {default}
     bool UseAdaptiveSizePolicyWithSystemGC        = false                                     {product} {default}
     bool UseDynamicNumberOfGCThreads              = true                                      {product} {default}
     bool UseG1GC                                  = true                                      {product} {ergonomic}
     bool UseGCOverheadLimit                       = true                                      {product} {default}
     bool UseMaximumCompactionOnSystemGC           = true                                      {product} {default}
     bool UseParallelGC                            = false                                     {product} {default}
     bool UseSerialGC                              = false                                     {product} {default}
     bool UseShenandoahGC                          = false                                     {product} {default}
     bool UseZGC                                   = false                                     {product} {default}

(2) 掌握常用工具

(3) 调优与代码、平台相关，无万能范式。